There are times during drilling operations, when it is necessary to alter the physical structure of a formation surrounding a wellbore. Examples of such physical alterations include fracturing operations, loss circulation control, and shale formation inhibition. Fracturing operation operations are proactive methods to increase the amount of hydrocarbons recovered from a formation. Conversely, loss circulation control and shale formation inhibition are defensive measure to prevent reductions in recovery.
Loss circulation, a partial or complete loss of drilling fluids into the formation, is a common and expensive problem in drilling operations. Loss circulation causes well control problems and unsafe well control conditions. When whole volumes of drilling fluids are lost into the formation, additional volumes of drilling fluid must be mixed to make-up for the losses. Thus, the occurrence of a loss circulation zone increases the costs associated with drilling the well and results in lost product time.
Loss circulation occurs due to fractures caused by mud weight/pressure, formations with high permeability and porosity, and natural fractures or caverns. In complete loss circulation, the wellbore opens and the pressure exerted by the mud column disappears creating an under balance situation, where the formation fluids enter the wellbore and cause a kick.
To combat loss circulation, lost circulation materials are used to plug the opening in the wellbore. Loss circulation materials can be whole fluids delivered separately to the loss circulation zone, such as cements, or can be fluid additives mixed with the drilling fluids. Conventional fluid additives include chemical reactants and particles that are mixed with the mud, such as husks, fibers, or other solids such as calcium carbonate. Chemical reactants often have delayed reaction pathways, such that the reactants can be mixed in together at the surface, but the reaction does not proceed until the reactants reach the loss circulation zone.
Problems with current lost circulation materials include cement jobs that fail to plug the loss circulation zone and compromise the integrity of the casing requiring future remedial work. Solid additives that are too small to have effect in large loss zones are also a problem. Chemical reactants that react too quickly or too slowly to plug the loss zone are also common problems. Loss circulation materials that require precise placement add to the delay time of drilling. Loss circulation materials which can be efficiently placed and will act to block the entire loss circulation zone are desired.
Shale formations are commonly encountered during drilling operations. Shale contains clay materials, along with other minerals. Water in the drilling fluids interacts with the shale to cause shale swelling, sloughing, and can even lead to well collapse. The shale absorbs water from the drilling fluids and increases in weight and dimension. By some estimates, 70 percent (%) of wellbore instabilities are associated with shale formations. The instabilities pose safety risks and increase well costs.
Shale swelling is usually addressed by adding shale inhibitor materials to the drilling fluids at the surface, the inhibitors interrupt the interaction between the shale and the water. The drilling fluids with shale inhibitor materials are then pumped to the thief zones to prevent the shale swelling. Inhibitor materials are expensive. Additionally, inhibitor materials have environmental limitations and pose problems for disposal.
Conventional methods of addressing loss of circulation and shale formations use different treatment systems. These different treatment systems incur costs and can take time to change back and forth between the two.
Therefore, a product that alters the physical structure of the formation without such drawbacks is desired.